The present invention relates generally to apparatus for adjusting the relative humidity of gas to a fixed value and, more particularly, to apparatus for maintaining and controlling humidity and moisture levels at constant values within small volume closed containers.
Systems utilizing saturated aqueous salt solutions for controlling and maintaining humidity of a gas within a closed space are known. These systems have numerous applications, such as in conducting long-term (e.g., two years) compatibility tests of materials. For example, it may be desirable to determine whether two dissimilar metals, joined together in a mechanism, experience corrosion when exposed to moisture within an operating environment.
In conducting material compatibility tests, it is important that humidity be kept at a constant value, meaning that pressure and ambient temperature of humidified gas must be precisely controlled. Also, since these material compatibility tests are of long-term duration, it is preferable to employ a testing system wherein the saturated salt solution does not have to be replenished, as would be required in the humdifier disclosed in U.S. Pat. No. 4,406,843 to Nakamura et al.
Of particular importance when conducting compatibility tests is the exclusion of solids, such as salt particles, from the immediate test environment. In less desirable humidification devices utilizing saturated salt solutions as a vapor source, problems have occurred in long-term testing due to migration of the salts. Somehow these salts migrate from the bottom of a test container, up the container side walls, and into the environmental test region. Obviously, the presence of salt particles and other undesirable substances within the test region tends to cause corrosion of test materials, destroying the validity of the tests.